tag-information

Arguments:
name &optional env

This function returns information about the tag named by
name in the environment
env. env may an environment
object or nil, indicating the null lexical
environment.

Three values are returned: :tag, a locative, and
declaration list. The car of the locative is a catch tag (usually a
unique cons cell) for throwing to its target in the interpreter, and
the cdr of the locative is the portion of the interpreted code that
immedately follows the tag in the code.